Process oe treating lead alloys



PATENT OFFICE.

JAMES O. J'OHNSTONE, OF EAST CHICAGO, INDIANA.

PROCESS OF TREATING LEAD ALLOYS.

In Drawing.

To all whom it may concern:

Be it known that I, JAMES O. JOHNSTONE, a citizen of the United States of America, residing at East Chica o, in the county of Lake and State of lmfiana, have invented certain new and useful Improvements in P8 of Treating Lead Alloys, of which the following is a specification.

The resent invention relates to an economic method of treating lead bullion, that is to say, lead containing some quantities of other materials, such as silver, antimon copper, bismuth and the like, with the pro notion of pure lead compounds on the one hand and the complete quantity of other constituents of the initial material, either in a pure state or in a highly concentrated state, as compared with the starting material, on the other hand. The process of the present invention is particularly useful in connection with the treatment of lead bullion containing from 3 to 5% of antimony, together with varying quantities of the other metals above referred to, which material is diflicult to treat according to existing methods on account of the expense involved.

In accordance with the process of the present invention, I first preferably comminute the bullion and this can be readily accomplished in a number of ways. The preferred mode is to melt the material and atomize the same by a blast of air or steam or to break up the molten material into relatively fine particles, although any suitable mode of comminuting the material may be em loyed.

e comminuted material is then treated hot with a solution of lead nitrate. This operation is preferably carried out at a temperature near the boiling point, although a. temperature of from 80 to 90 C., gives excellent results. The comminuted lead material is allowed to stand with the hot lead nitrate solution while agitated in any desired manner, until the bulk of the lead nitrate present has been converted into basic lead nitrite.

The strength of the lead nitrate solution may vary considerably, but I find that a solutlon of about 8% gives excellent results. The liquor may however contain substantiall more than this, say 10 to 12% if desirel The metals other than lead, present in the bullion will not be dissolved by this treat- S peciflcation of Letters Patent.

Patented Aug. 30, 1921.

Application filed August 9, 1920. Serial No. 402,223.

ment, but will remain in the liquor in the form of a slime. The slime can be removed from the liquor by settling in a suitable thlckener and the thickened slime filtered preferably while hot, and the residue on the filter is preferably washed with hot water. The supernatant liquor and the filtrate together with the washings, are then conveyed to a suitable cooling tank or receptacle in which the mixture is allowed to cool. Basic lead nitrite or a double compound of basic lead nitrite and basic lead nitrate will crystallize out on cooling, these compounds being not very soluble, particularly in a cold llquor. The liquid may be cooled during this operation to, say, 35 C. There are a number of basic compounds of lead nitrate and of lead nitrite, and also a number of double compounds of the two materials, and the exact composition of the product of this cooling operation will depend upon a number of factors, such as the amount of cooling, the relative amounts of basic lead nitrate and basic lead nitrite in the solution and the degree to which the reduction of lead nitrate has been carried by treatment with metallic lead.

The lead compounds produced will be substantially free from antimony, silver, bismuth and the like, which were present in the original bullion.

The reaction between the lead nitrate and the lead of the bullion may be continued until a desired amount of the nitrate has been converted into basic nitrite. Since the reaction slows down considerably as the concentration of the lead nitrate in the solution decreases, it is usually advisable to draw ofl when 75 to 85% of the lead nitrate has been so converted.

It is, of course, not necessary that all the lead present in the alloy be dissolved from a given batch of the comminuted bullion in a single treatment with lead nitrate. After the first liquor is drawn off, one or more subsequent treatments with lead nitrate solution can be given, and the process continued until the lead content is reduced to any desired figure (or stated another way, until the content of metals other than lead has been raised to any desired figure).

The basic nitrlte or crystallized material may then be worked up in any one or a number of different methods, as described below,

and the liquor can be worked over (i. 0.,

oxidized) to again form a solution of lead nitrate for use in treating a further quantity of the comminuted bullion or alloy The basic lead nitrite can, if desired, be converted into litharge, for example by a roasting or heating operation, the said material being heated with access of air up to atemperature substantially above 200 (1., and in order that the decomposition may be complete, it is advisable to carry the temperature up to 400 or even 425 C. Ordinarily, it is advisable not to carry the temperature beyond the melting point of 11th- ,arge (about 888 C9).

The oxids of nitrogen given off during the heating of the basic nitrite can be suitably used in the regeneration of lead nitrate so ,lution. The said fumes, mixed with air, can be led into an absorption apparatus in which they are absorbed in water to produce nitric acid, or preferably the said fumes mixed with air can be absorbed by the solution from which the lead nitrite has been crystallized and which ordinarily will contain a substantial amount of lead in solution. Thus I can first treat the fumes with water in such a way as to produce relatively concentrated nitric acid and the residual fumes are then treated with the mother liquor from the crystallization. In order to make up for mechanical losses of nitrous fumes, the furnace in which the basic lead nitrite is decomposed, may be heated by an electric arc, in which event there will be produced some compounds of nitrogen and oxy- I gen from the air and the OXlClSOf nitrogen thereby produced travel along with the oxids of nitrogen produced by the decomposition of the basic nitrite to the absorption apparatus.

In place of producing litharge, red lead can be produced by careful regulation of the temperature to which the basic lead nitrite is heated, a sufficient excess of air for the oxidation being present.

In another modification of the process, the basic lead nitrite solution, after removal of the slime, may be employed for the production of white lead. In this form of execution of the process, it is advisable that the strength of the solution be about 8% and for this purpose a small proportion (say about the basic lead nitrite may be allowed crystallize out. Thesolution is then treatedw th gases contaming carbon dio zgid, purified products of combustion being suitable for the purpose. This operation precipitates basic lead carbonate or white lead, which can be separated from the solu tion by filtration, sedimentation or other appropriate method. The press cake can be washed, dried and ground in the usual manner, as in the ordinary preparation of white lea-d. There remains solution containing merely as a carrier of the oxygen of air to the nitrite to produce nitrate, it is not necessary to have a large excess of oxids of nitrogen, but the solution entering the absorption tower should be sufficiently basic to catch the nitrogen peroxid before the same leaves the tower.

Before treating the basic lead nitrite solution with gases containing carbon dioxid, it may sometimes be advisable to add a small amount of acetic acid tolthe liquor, basic lead acetate being substantially more soluble than the basic nitrite. This, however, is not essential.

The physical character of the white lead can be regulated by the percentage .of carbon dioxid, strength of solution, temperature of the treatment, in the same manner as in the other precipitation processes for. making white lead.

Other salts of lead, instead of those-above referred to, can be produced by suitable treatment ofthe crystallized basic lead nitrite.

In another modification of the process, the litharge produced can be reduced by heating withcarbon as in the usual well known manner, to form pig lead.

The slime, as above noted, contains substantially the whole of the silver, antimony and a portion of the lead contained in the original raw material. This slime can be worked up in any appropriate manner and for'the purpose of illustration, the following is given: a

The slime from the filter, after washing, is dried and melted ina reverberatory furnace, The antimony slag which forms should be tapped off and more slime charged, this being repeated until there is enough rich bullion left to be cupelled for silver..

When the antimony slag contains too much silver to be used in making hard lead, I it may have a second treatment in the reverberatory furnace along with some coal'to free it from excess of silver, and some galena ore to free it from copper; The'litharge from the cupellation should be treated in this furnace also. The slag may then be sent to the blast furnace to be smelted from antimonial lead.

While the process has been .described'as 5a lead nitrite usually containing some lead lead and at least one of the mctals'antimony, 30

silver and bismuth, the herein described improvement which comprises treating the said bullion in a comminuted state with a solution containing lead nitrate, until a substantial proportion of the said lead nitrate has been converted into basic lead nitrite, and separating the slimes containing the antimon silver and bismuth content of the bullion rom the solution containing lead nitrite.

2. A rocess which comprises corroding impure ead in the form of relatively small pieces by means of a solution of lead nitrate, whereby basic lead nitrite is produced, and separating such solution from any undissolved excess of lead and foreign metals.

3. A process for the treatment of metallic material containing lead, which comprises corroding the metallic material in the form of relatively small ieces, by agitating the same with a hot so ution containing lead nitrate, until the major part of the nitrate has been converted into basic lead nitrite, separatin the hot solution from any undissolved residue, cooling the liquid to cause the crystallization of material comprising basic lead nitrite, heating such crystallized material to produce lead oxid, and recoverin the oxids of nitrogen evolved in such heatlng operation.

In testimon whereof I afiix m signature.

AMES 0. JOH STONE. 

